1. Field of the Invention
The present invention generally relates to subsea equipment for oil and gas production. More particularly, it relates to subsea blow-out preventers (BOPs) and other such hydraulically actuated equipment.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A blow out preventer is a piece of hydraulically operated equipment used to close in a well (in an emergency) fitted around a drill string or production riser.
In essence, a BOP is a large valve at the top of a well that may be closed if the drilling crew loses control of formation fluids. By closing this valve (usually operated remotely via hydraulic actuators), the drilling crew usually regains control of the reservoir, and procedures can then be initiated to increase the mud density until it is possible to open the BOP and retain pressure control of the formation. BOPs come in a variety of styles, sizes and pressure ratings. Some can effectively close over an open wellbore, some are designed to seal around tubular components in the well (drillpipe, casing or tubing) and others are fitted with hardened steel shearing surfaces that can actually cut through drillpipe. Since BOPs are critically important to the safety of the crew, the rig and the wellbore itself, BOPs are inspected, tested and refurbished at regular intervals determined by a combination of risk assessment, local practice, well type and legal requirements. BOP tests vary from daily function testing on critical wells to monthly or less frequent testing on wells thought to have low probability of well control problems.
Although typically controlled from the surface via umbilical lines, subsea BOPs often are equipped with a hydraulic port for connection to an underwater remotely operated vehicle (ROV). In this way, if the BOP cannot be closed via the surface controls, hydraulic fluid (under pressure) supplied by an ROV connected to the BOP control circuits may be able to close the BOP.
In any subsea hydraulic connection, there is a risk that seawater may enter the hydraulic system and contaminate it and there is a risk that hydraulic fluid may leak out of the hydraulic connection and contaminate the marine environment. In the past, ROV ports have been plugged, manual valves which can be actuated by a ROV have been used, and conventional single check valves have been used to address this problem. None of the previously tried solutions mentioned above will permit return flow out of the ROV port. The present invention addresses this problem in a novel way.